This invention relates to a method and apparatus for forming a flexible, reinforced plastic sheet material of indeterminate length and more particularly relates to forming a laminated plastic sheet material made from two films of a multi-layer thermoplastic material and a rectilinear web of machine-direction (MD) and transverse-direction (TD) strands or films which are simultaneously laid down between the films.
Shipping sacks are used to store and ship 25-100 pound commodity lots of many diverse materials: for example, grain, cement, fertilizer, peat moss, minerals, chemicals, plastic resins, etc. Bulk sacks are used for shipping and storing much larger quantities of many of these same materials. Among the numerous component materials which are used for such sacks are single-ply 4-10 mil LDPE or LDPE/HDPE co-extruded film and cross-laminated MD-oriented HDPE film. Reinforced composite sheets are also available for such sacks, as described, for example, in U.S. Pat. No. 4,161,559.
Other uses for reinforced composite sheets are coverings for greenhouses, barns, buildings under construction, and commodities which must be stored in the open. The reinforcing material may be in the form of a non-woven or pre-woven scrim or woven mesh material having openings between the strands that are wider in inverse proportion to the severity of the loads to be met. Such a reinforced composite sheet is described in U.S. Pat. No. 3,616,130.
Methods for producing reinforced composite sheets include the layering of a scrim between a pair of flexible films (U.S. Pat. Nos. 3,186,893; 4,088,805; and 4,106,261) and the formation of a woven or non-woven pattern of MD and TD fibers simultaneously with or immediately prior to the layering operation (U.S. Pat. Nos. 1,914,801; 3,169,087; 3,272,679; 3,414,453; 3,496,053; 3,511,739; 3,686,062; and 3,950,583).
Non-woven patterns may be sinusoidal (U.S. Pat No. 1,914,801), MD/TD grid (U.S. Pat. No. 2,851,389), or helical (U.S. Pat. Nos. 3,169,087; 3,272,679; 3,332,823; and 3,332,824). Apparatuses for forming such non-woven patterns include the following diverse arrangements: (a) an endless reciprocating tape and guide bar arrangement for forming a cyclically deposited web (U.S. Pat. No. 3,272,679); (b) a rotary apparatus for winding a helix of strands around a pair of endless carriers having opposed and substantially parallel reaches (U.S. Pat. Nos. 3,332,823and 3,332,824); (c) a horizontal rotary drum mounted above a rotating table at the top end of a post carrying plastic strands for making laminated webs of filamentary reinforcing material (U.S. Pat. No. 3,414,453); (d) a positioning plate for moving warp strands under tension imparted by creel-and-tension carts about the surface of a cylindrical support while adhesively coated fill strands are wound about the warp strands to form a tubular web of fabric (U.S. Pat. No. 3,496,053); (e) a plurality of strand guide bars carried by a reciprocating tape and operated simultaneously in reciprocating movements, with a phase shift of 180.degree. between the guide bars, to produce an array of reinforcing strands having sinusoidal configurations with multiple overlap patterns (U.S. Pat. No. 3,511,739); and (f) a fixed creel containing reels in two parallel rows making a first lap of warp threads, a rotary creel containing a series of reels spaced apart about the circumference of a coaxial circle, an elongated comb for distributing the warp threads into a plane, a circular plate for winding the weft threads into an annular lap in flattened spirals about the lap of warp threads, and cutters for opening up the annular lap (U.S. Pat. No. 3,950,583).
Co-axially extruding two different thermoplastic materials to form a single annular extruder die to form a duplex film by the blown tube method is described in U.S. Pat. No. 3,223,761 and 3,467,565. Various combinations of polymers and co-polymers in multi-layered duplex plastic sheets, having differing melting points in the inner and outer layers for bonding by heat and pressure to a web of reinforcing material therebetween, are described in U.S. Pat. No. 3,616,130.
Many of these processes produce composite sheet materials having excellent strength properties, but the materials have such excessive thicknesses or the processes operate at such slow speeds or are afflicted with so many maintenance or adjustment problems that costs are excessive. In consequence, shipping sacks made from plastic film have thus far been utilized in a small fraction of the shipping sack/packaging business.
Accordingly, a thinner composite sheet having adequate strength and other physical properties at a basis weight that is at least 30% less than the weight of presently available composite sheets is needed.
A simpler on-machine method and an apparatus for forming a reinforcing grid and for bonding the grid to the film on either side thereof to form the thinner composite sheet at lower cost are equally needed.
Additionally, a method of bonding this novel sheet along the edges thereof to form a tubular article, in order to retain the desirable properties of central portions of the sheet, is also desirable in order to obtain shipping sacks with uniformly suitable properties.
It is therefore an object to provide a composite film sheet of indeterminate length, having a selectively high strength at a basis weight which is approximately 30% less than that used in shipping sacks at the present time.
It is also an object to provide a composite film sheet comprising two films and a reinforcing grid in which the transverse-direction film is continuous, is in parallel reaches at a selected spacing between the reaches, and has 180.degree. loops connecting the ends of the reaches and disposed entirely within and between the films.
It is additionally an object to provide a grid of machine-direction fibers, having a selected first strength/weight ratio and a selected first spacing between the filaments, and a single transverse-direction fiber which has a selected second strength/weight ratio and is disposed transversely and adjacent to the machine-direction fibers as parallel reaches which: (1) are connected sequentially by loops, (2) have a selected second spacing between the reaches, and (3) are bonded to the MD fibers.
It is further an object to provide a fiber-reinforced composite film sheet of indeterminate length, comprising a pair of co-extruded film sheets which are disposed in straddling relationship to the MD fibers and TD fibers so that each film sheet comprises an outer layer having a low softening temperature, whereby the pairs of film sheets, the MD fibers, and the TD fiber are bonded together under heat and pressure.
It is still further an object to provide an fiber-orienting apparatus for continuously forming a single fiber into a plurality of transverse-direction reaches which are connected at the ends thereof by 180.degree. loops.
It is also an object to provide an apparatus for continuously juxtaposing a pair of films, the machine-direction fibers, and the looped transverse-direction fiber into a sandwich.
It is another object to provide a means for removing the loops from the film-orienting apparatus without displacement of the loops and transverse-direction reaches within the film sheets.
In accordance with these objectives and the principles of this invention, a composite film sheet of indeterminate length, having a selectively high strength at a basis weight which is approximately 50% less than that used in shipping sacks at the present time, is provided. This composite film sheet comprises:
A. MD fibers having a selected first strength/weight ratio and a selected first spacing between the fibers;
B. a single TD fiber which has a selected second strength/weight ratio and is disposed within the composite film as parallel reaches which:
(1) are connected sequentially by loops, PA1 (2) have a selected second spacing therebetween, and PA1 (3) are disposed transversely to the MD filaments; and PA1 (a) a central screw and nut which are attached to the arm, PA1 (b) a spindle shaft which coaxially surrounds the screw, PA1 (c) a pair of spindle bearings surrounding the shaft, and PA1 (d) a spindle body having a fiber-supporting portion and a tapered lift-off portion.
C. a pair of co-extruded film sheets which are disposed in straddling relationship to the MD fibers and the TD fiber so that the loops are enclosed between the film sheets, each film sheet comprising an outer layer having a high softening temperature, and an inner layer having a low softening temperature, whereby the pairs of film sheets, the MD fibers, and the TD fiber are bonded together under heat and pressure.
Preferably, the film sheets are co-extruded, and the inner layers are bonded to both the MD fibers and the TD fiber. If necessary in a particular combination of fiber and film compositions, an adhesive is added to the fibers. It is particularly suitable that such an adhesive be deposited on the MD fibers, such as by coating the fibers before usage thereof. However, it is further within the scope of the invention to coat the film sheets and the TD fiber, alternatively or additionally. It is also a part of this invention to utilize fibers in the form of co-extruded tape, having external layers of low-density polyethylene, whereby no adhesive is needed.
The continuous method of this invention for manufacturing a composite sheet material, having a combination of high strength properties and light weight, comprises the following steps:
A. continuously drawing a plurality of machine-direction (MD) fibers from bobbins within a creel;
B. passing these MD fibers in longitudinally foward movement through a comb and forming a first planar lap of parallel, longitudinally aligned fibers;
C. drawing a single transverse-direction (TD) fiber from a bobbin at a high linear velocity;
D. passing this single TD fiber between spindles within an interweaving section of a pair of endless, spindle-equipped chains which cooperatively comprise the interweaving section, a diverging section, and a parallel section while revolving in opposite directions as a pair of planar patterns which are parallel to the first planar lap;
E. engaging the single TD fiber around the successively interweaving spindles of the spindle-equipped chains to form a successive plurality of closely spaced loops when each spindle of one chain pulls the TD fiber toward and beyond the previously passing spindle of the other chain;
F. laterally extending the single fiber, by longitudinal movement of the inward sides through the diverging section, to separate transversely alternate loops in the plurality of loops and form two rows of loops and a plurality of closed spaced TD fiber reaches which are transversely disposed to the longitudinally aligned MD fibers and connected at ends thereof by the plurality of loops;
G. continuing to move the transversely disposed TD reaches and loops through the parallel section of the pair of chains;
H. drawing a pair of films from a supply thereof;
I. forwardly passing the pair of films in straddling and parallel relationship to the plurality of longitudinally extending fibers and the plurality of transversely disposed fibers;
J. converging the films, the TD reaches, and the MD fibers to form a fiber/film sandwich;
K. edge sealing the sandwich along each edge but inwardly of the adjacent row of loops;
L. withdrawing the loops from the spindles;
M. transversely stretching the withdrawn sandwich;
N. laminating the longitudinally extending films, the transversely disposed reaches and loops, and the pair of films to form the composite sheet; and
O. winding the laminated sheet.
The pair of films are suitably formed by slitting a flattened tube of extruded film, drawn from a roll thereof as the supply of step H, at the sides thereof. If the roll of extruded film is on approximately the same level as the laminating apparatus, each of the films is passed over a turning bar, whereby the drawing of step H and the forwardly passing of step I are perpendicularly related. The films are transversely stretched by passage through a lateral expansion means, after the turning operation.
Laminating the fiber/film sandwich inwardly of the loops, for holding the transversely disposed TD reaches and the MD fibers in place within the sandwich, forms a laminated strip on each side of the sandwich. Such strip laminating is done by two pairs of opposed heated rolls.
The withdrawing of step L is performed by a pair of cams which lift the loops from the spindles. The transverse stretching of step M is performed by transversely disposed rolls having frictional surfaces with respect to the films. The laminating of step N is performed by a pair of heated rolls.
The extruded film is suitably a co-extrusion of high-density and low-density polyethylene. Preferably, the high-density polyethylene is 25% of the film by weight, and the low-density polyethylene is adjacent to the fibers. The fibers are suitably coated with a pressure-sensitive adhesive. The MD and TD fibers may be in the form of monofilaments or may be MD-oriented polypropylene tape. Alternatively, polypropylene tape is extruded with low-density polyethylene, whereby lamination between MD and TD fibers and between the fibers and the film requires no adhesive.
The fiber-reinforced film sheet of this invention generally comprises a non-woven fiber network which is laminated between two layers of co-extruded plastic film. The machine-direction fibers suitably consist of five hundred-denier (0.050-inch wide by 0.002-inch thick) oriented polypropylene tape. The fibers are disposed a suitable distance apart within the first planar lap. This distance apart is in accordance with the strength required for end use of the film sheet. For example, they may be 0.375 inch apart, on centers. The transverse-direction fiber is disposed in a serpentine form, with adjacent reaches of the fiber disposed 0.375-inch apart, also measured on centers, as an exemplary distance apart. The three-eighths inch spacing between MD and TD fibers is one specific example which is widely useful, but many other spacings are feasible and highly suitable for particular applications. The MD fibers and the TD fiber are generally both polypropylene. Polypropylene tape is one highly satisfactory embodiment, but monofilaments and multi-filaments of polypropylene and other high strength polymers can be used to form specific products having certain desired properties.
Polypropylene in the form of tapes, fibers, and filaments which are oriented in the machine-direction for optimum strength properties are well known. When in the form of a single homogenous product that is extruded and drawn from a round die orifice, a monofilament is produced which has high strength (75,000 psi) and medium cost. When extruded from a flat die and slit into narrow widths in the machine-direction and MD oriented, polypropylene tape is produced, having medium strength (50,000 psi) and low cost. This type of polypropylene fiber is the most widely used in the textile industry at the present time. When extruded from a multitude of fine holes (spinerette) and spun into the finished yarn, a multi-filament strand is produced which has a number of fibers in the strand (e.g., 50), producing a yarn of conventional appearance, much greater flexibility than the monofilament, and wider usefulness in regular textile applications. This product has medium strength (45,000 psi) and a higher price than either the monofilament or the polypropylene tape.
The tubular co-extruded film is 1.5 mil thick and comprises 25% high-density polyethylene (HDPE) and 75% low-density polyethylene (LDPE). The collapsed tube is slit at the sides or edges to form the pair of single-layer films. In addition to polyethylene as the raw material for the co-extruded film, liquid or gas barrier materials, such as nylon and films of heavier gauges or lighter gauges, are useful.
A suitable apparatus for manufacturing the fiber reinforced or composite film sheet of the invention comprises:
A. a machine-direction multi-fiber feeding assembly;
B. a transverse-direction single-fiber feeding assembly;
C. a fiber-orienting means for forming the single fiber into a plurality of transverse-direction reaches which are connected by loops at the ends thereof and move in the machine direction at the same speed as do the machine-direction fibers;
D. a film feeding assembly for a pair of co-extruded films of indeterminate length which are arranged in straddling relationship to the MD and TD fibers;
E. a converging assembly for the machine-direction and transverse-direction fibers and the pair of films to form a fiber/film sandwich;
F. a high-temperature nip roll system for laminating the fiber/film sandwich together to form the fiber-reinforced film sheet; and
G. a winder for winding the laminated fiber-reinforced film sheet into a roll.
The apparatus further comprises:
A. a pair of expander rolls for smoothing and widening the pair of films in the transverse direction, prior to reaching the converging assembly; and
B. an edge sealing assembly for heat sealing the pair of co-extruded films of the sandwich to the transverse-direction reaches within a pair of strips which are disposed close to the loops at each edge but inwardly of the loops, whereby the fiber/film sandwich is conjoined within the two strips.
This fiber-orienting means is an apparatus comprising a pair of endless roller chains which are disposed to revolve in a pair of elongated patterns within a common plane. The opposed portions of the patterns move forwardly and comprise an interweaving section, a diverging section, and a parallel section. Each roller chain comprises a triple strand of linked rollers and a row of spindles which are attached to but are laterally offset from the rollers to project outwardly from the pattern.
Each triple strand roller chain comprises pin link plates, roller pins, straight lug link plates, spindle arms attached to the straight lug link plates, and spindles which are rotatably attached to each arm. Each spindle comprises a spindle body having a convex groove for tracking the TD filament. The groove has a crown angle at its center of about 5.degree.. The spindle body further comprises a tapered fiber lift-off surface having an angle of about 45.degree. to the axis of the spindle.
The fiber-orienting apparatus, for producing the TD fiber reaches and loops, more specifically comprises a pair of endless roller chain assemblies which each comprise:
(1) a triple-strand roller chain,
(2) a row of chain attachment plates,
(3) a row of spindle arms, each arm being riveted at one end to one of the attachment plates and extending transversely to the roller chain,
(4) a row of spindles, each spindle being attached to the other end of a spindle arm, and each spindle comprising:
The chain system comprises a plurality of spindles lying within a common plane on which the loops are held. For lifting each row of loops from the spindles after passing the edge sealing assembly, a cam means is provided in cooperation with an overlying idler roll which enables the nip rolls to function as an elevating means for directing the fiber/film sandwich obliquely to the common plane in which the spindles revolve.
Two pairs of edge pulling brushes and two pairs of short Mt. Hope rolls are also incorporated into the apparatus in order to stretch the fiber/film sandwich in the transverse direction before reaching the high-temperature nip roll system.
The method for making this fiber-reinforced composite film sheet and the apparatus for carrying out this method are both inherently flexible. The method has flexibility as to adjustable width of the composite film sheet, for example, because the apparatus includes means for selectively moving the pairs of bushing chain assemblies, nip roll systems, loop disengagement devices, and edge pulling devices toward or away from each other. To achieve this flexibility, the idler sprockets on the inner side of the chain loops, the converging assembly, the edge sealing rolls, the loop release cams, the edge pulling brushes, and the tautening rolls are all mounted on a pair of frame plates which are transversely movable relative to the frame of the laminator for changing the width of the composite film sheet without changing the overall pitch length of the chain assemblies.
The method is also flexible as to construction features of the composite film sheet in order to achieve acceptable performance of a film/laminant bag in any specific application by tailoring the strength properties of the composite film sheet so that the bag can pass the requisite performance tests for its type, such as progressive drop, 6-sides drop, and creep. Such construction flexibility can be obtained by using fibers containing various desired proportions of high- and low-density polyethylene, polypropylene, polyamides, polyesters, polystyrene, polyacrylonitriles, polyvinyl chloride, rayon, cotton, wool, and other synthetic and natural fibers, including copolymers, and the like. The denier of the fibers, the center-to-center spacing therebetween, and the adhesive for bonding MD fibers to TD fibers and for bonding both fibers to the films can also be varied. In addition, low-density polyethylene can function as a heat-activated adhesive if co-extruded as the outer layer for a polypropylene fiber core. Futher flexibility of construction can be obtained by varying the type of polymer, its crystallinity, the thickness of the films, and the proportions of polymer types if a layered film construction is selected, such as 25% high-density polyethylene and 75% low-density polyethylene.
The film sheet of the invention may be converted into a tube either by sewing or by hot-melt gluing along the edges, provided that there is sufficient overlapping that the rows of filament loops are in overlying relationship to provide a seam having the equivalent strength of the body of the laminate. This tube may then be fed to a bag-making operation which can produce bags of desired sizes and strength properties by sewing or gluing along the bottom and top edges of the bags.